Patients with advanced age-related macular degeneration in one eye and early age-related macular degeneration in their fellow eye will have their fellow eye evaluated over a three year interval with computer-assisted maps of macular malfunction, Amsler grid testing, blue-cone thresholds in the fovea, and foveal cone electroretinograms. Results will be compared with the appearance of the macula in the fellow eye quantified from optically- scanned fundus photographs and fluorescein angiograms to determine to what extent changes in these macular function tests correspond with changes seen in the fundus on the same or subsequent visits and precede the development of exudative maculopathy and/or loss of visual acuity. In separate sets of patients with early stages of either age-related or juvenile macular degeneration, cone and rod dark adaptation kinetics will be assessed with long and short duration bleaches in regions of the macula outside the foveola to help determine if the retinal pigment epithelium or the photoreceptors, or both, are primarily involved, and to evaluate whether rod malfunction precedes cone malfunction in these regions. This research should provide a better understanding of pathophysiological mechanisms that may be involved in these conditions. In the case of age-related macular degeneration, macular degeneration, demonstration of the usefulness of one or more of the functional tests under study in detecting more patients with impending exudative maculopathy and loss of visual acuity may increase the number of patients who would subsequently benefit from laser therapy.